错误原因：
如API中所述
API：
A table of data representing a database result set, which is usually generated by executing a statement that queries the database. A
ResultSet object maintains a cursor pointing to its current row of data. Initially the cursor is positioned before the first row. The
next method moves the cursor to the next row。
就是说游标初始化的位置在首行之前。
解决方法：
在使用rs前要调用rs.next()方法
java.sql.SQLException: Before start of result set,布布扣,bubuko.com